A lithography machine is one of the most important ultra-precision equipment in nanometer scale integrated circuit manufacturing. A double-workpiece-stage is one of the key subsystems of the lithography machine and greatly determines the resolution, precision and productivity of the lithography machines.
Productivity is a main goal that pursued in the development of lithography machines. When the resolution, accuracy and efficiency requirements are fulfilled, productivity of the lithography machine is a development direction of the wafer stage technology. The most straightforward way to improve operating efficiency is to improve the acceleration and the velocity of the wafer stage, however, unlimited increase of the acceleration and the velocity will reduce the original precision. The wafer stage was initially designed with only one silicon wafer fixing device, the lithography machine can only manufacture one silicon wafer in a serial process which results in a low productivity. A double-workpiece-stage system is then proposed, which is so far the prevailing technical means to improve productivity of lithography machine. The double-workpiece-stage system is equipped with one exposure station, one measurement station and two wafer stages. Exposure and measurement adjustments can be processed in parallel, which can greatly reduce time and improve production efficiency. A representative product is a double-workpiece-stage lithography machines based on Twinscan technology provided by ASML Company in the Netherlands.
Currently, improving the operating efficiency of a double-workpiece-stage system is one of the technical development goals for lithography machines. Double-workpiece-stage technology involves the transposition of two wafers between the two stations. The transposition efficiency directly affects the operating efficiency of the system and consequently the lithography productivity. How to reduce transposition time of a double-workpiece-stage system and minimize the interference on other subsystems has always been a focus of study. In conventional double-workpiece-stage transposition processes, the double-workpiece-stages are driven linearly in both the exposure and measurement processes. In US2001/0004105A1 and WO98/40791, which are double-workpiece-stage system related patents, each wafer stage has two exchangeable units to achieve the double-workpiece-stage transposition process. This arrangement can improve productivity of the machine without increasing the operating speed of the double-workpiece-stage. However due to the coupling connection between the work station and the rail, the double-workpiece-stage will temporarily separate from the driving unit in the process of transposition, which will have considerable influence on the positioning accuracy of the double-workpiece-stage. At the same time, as the movement unit and the guide rail longer and the mass of the moving parts are greater, it may adversely affect the enhancement of movement speed and acceleration. Chinese Patent No. CN101609265 proposes a double-workpiece-stage switching system based on planar motor driven, in which a stator of the planar motor is arranged on the top of a base stage and a mover is arranged at the bottom of the double-workpiece-stage. The double-workpiece-stage and the driving unit are never separated from the linear motor drive. In Chinese Patent No. CN101694560, a double-workpiece-stage transposition system driven by airfoil support permanent magnet planar motor is proposed, in which the wafer stage is driven by a planar motor and supported by airfoil to avoid the problem that the driving units and the double-workpiece-stage may separate during the transposition process. Meanwhile, the running resistance of the double-workpiece-stage and the drive current and the heat of the planar motor are reduced.
Compared with the linear transposition strategy of double-workpiece-stage mentioned in the above patents, revolving transposition strategy of wafer stages has a unique advantage, and dual-stage with the revolving transposition technology emerged. Chinese Patent No. CN101071275 adopts the method of revolving the whole pedestal to realize the transposition of the two wafer stages. This arrangement can simplify the structure of the system, and the movement of the two wafer stages is not overlapping with each other, thereby potential danger such as collision can be avoided. However, when the whole pedestal is revolved to achieve the wafer stage transposition, problems such as large revolve inertia, imprecise position of the high-power revolve motor, and the system temperature rising due to greater heat generation may arise. Meanwhile, the larger radius of revolve increases the dimension of the main structure of the lithography machine. Chinese Patent No. CN102495528, the invention adopts a revolve transposition table in the center of the base station to complete the transposition process of the two wafer stages, which is divided into three steps, but the revolve position accuracy is low.
There are many sensors in the double-workpiece-stage. Traditional double-workpiece-stage uses cable transmission energy model or battery to supply energy model for the sensors. For the use of cable transmission energy model, the dragging effect of the cable affects the positioning and reduces the accuracy of the micro-movement-stage. For the use of battery power supply mode, the weight of the battery affects the resolution, accuracy and efficiency of photolithography, so it is not a good choice.